The present invention relates to a turbomolecular pump, and more specifically, to a turbomolecular pump in which a temperature of a rotor blade can be detected, thereby making it possible to prevent an abnormal increase in the temperature of the rotor blade, as well as to prevent the deposition thereon of generated products, to increase pressure upon baking, to provide an alarm of the extraordinary operation of the rotor blades, and to improve the exhaustion performance.
A turbomolecular pump is a vacuum pump in which rotor blades rotating at high speed and having blades at plural stages, which are divided in a circumferential direction, impart a certain momentum to a gas molecule impinging upon the surface thereof, to transport the gas. This type of pump is also used as a part of semiconductor manufacturing equipment.
Conventionally, when a turbomolecular pump is used to discharge an active gas or the like, a reaction with the active gas may cause generated products to be solidified or adhered. These generated products described above were in a state liable to solidify or adhere particularly when the temperature was low around the exhaust port. Therefore, as shown in FIG. 12, a temperature sensor 21 (e.g., thermistor) is embedded in a base portion 13, and is managed so that a temperature of the base portion 13 is kept constant in response to signals of the temperature sensor 21 (hereinafter referred to as TMS: Temperature Management System).
Degassing (hereinafter referred to as baking) from the turbomolecular pump, a piece of semiconductor manufacturing equipment and from a pipe connected therewith are carried out under such a state that they are heated to a certain temperature for a certain time period before the turbomolecular pump is operated. Thereafter, when the temperature is returned to an ordinary temperature, the degree of vacuum at a portion of an inlet port of the turbomolecular pump and an inside of a chamber may be increased (a so-called utmost pressure will be increased).
In addition, as shown in FIG. 12, the conventional turbomolecular pump includes a motor M driven by a motor driver 8 that is equipped with an r.p.m. sensor 2 for detecting an r.p.m. of the motor M, a motor current sensor 3 for detecting a current of the motor M, and an axial electromagnet current sensor 4 for detecting a current of an axial electromagnet causing the rotor blade to magnetically float.
An r.p.m. comparator 7 is connected to the r.p.m. sensor 2, and outputs a difference between an output of the r.p.m. sensor 2 and a set r.p.m. to the motor driver 8 via a set r.p.m. adjuster 11. With such an arrangement, the r.p.m. of the motor pump can be controlled.
Meanwhile, if the temperature of the rotor blade exceeds a long-term allowable heat-resistant temperature (e.g., 150xc2x0 C. when a material of the rotor blade is aluminum alloy), there is a concern that the strength of the rotor blade may particularly be lowered because of damage caused by heat generation, resulting in breaking the turbomolecular pump in the worst case.
Generally, when an output of the motor driver 8 is large (a maximum level of the current is made large, and is rated at 500 W, for example), this large output (because of output allowances) allows the r.p.m. not to be reduced even when a gas load is made larger. However, on the other hand, heat generation at the rotor blade becomes larger, with the result that the rotor blades deteriorate or are lowered in their strength due to the heat generation.
To cope with this, the output of the motor driver 8 was typically lowered to, e.g., 400 W to be set, and if the gas load exceeds an allowable value, the r.p.m. of the rotor blades is slightly lowered from the allowable rating. As a result, deterioration of the rotor blades caused by heat generation could be prevented.
In addition, an allowable flow rate is experimentally calculated, and determined so that the temperature of the rotor blade may be set within the allowable value even when the turbomolecular pump is operated for a certain time period.
In addition, in order to prevent an abnormal increase in the temperature of the rotor blade, a temperature sensor 23 (e.g., thermistor) is disposed in the vicinity of the motor M. When the temperature sensor 23 senses a certain level or more in the temperature, the turbomolecular pump is caused to stop immediately.
However, the conventional apparatus does not monitor the temperature of the rotor blade, and there are such disadvantages as will be described below. That is, the higher a set temperature of the TMS that is set, the smaller the deposition of generated products, so that the set temperature is preferably set as high as possible. If the set temperature is set as high, however, the temperature is elevated around the rotor blade, and heat radiation is prevented at the rotor blade. This results in a higher temperature of the rotor blade, a shorter lifetime of the rotor blade, a breakage, etc. Accordingly, there is a limit on increasing the set temperature of the TMS.
Further, similarly, if baking is carried out at a higher temperature, the utmost pressure is further improved, so that baking is preferably carried out at a temperature as high as possible. When baking is carried out at an excessively high temperature, however, the temperature of the rotor blade is elevated, and the heat generation may cause the lifetime of the rotor blade to be shortened.
In addition, even in the case where the temperature of the rotor blade is lower than an allowable heat-resistive temperature (within a sufficient allowance), if the turbomolecular pump is used under a reduced driver-output, the r.p.m. of the rotor blade is lowered (e.g., from normal 35,000 rpm to 33,000 rpm) with an increase of the gas load, thereby causing the exhaustion or exhaust performance to be deteriorated. The exhaustion performance in this case means that the exhaustion speed is lowered or an exhaust port pressure is increased. In other words, the higher the r.p.m. of the rotor blade is, the more the exhaustion performance is enhanced.
Moreover, if the gas load abruptly changes, the r.p.m. of the rotor blade is likely to fluctuate as the driver output is low, and therefore the exhaustion speed and the inlet port pressure may not be stabilized.
Further, there is a fear that even with the reduced driver output, the rotor blade may be gradually heated to have a high temperature as a long time elapses. In any event, there has been a need for measuring the temperature of the rotor blade to prevent deterioration of the rotor blade caused by the heat generation.
The present invention has been made in view of such conventional problems, and an object of the invention is to provide a turbomolecular pump in which a temperature of a rotor blade, etc., can be measured.
Another object of the invention as set forth in claim 6 is to provide a turbomolecular pump in which deposition of generated products can be prevented more effectively than in the conventional pump.
Still another object of the invention is to provide a turbomolecular pump with an improvement in an utmost pressure by increasing the utmost pressure when baking is performed.
Yet another object of the invention is to protect a turbomolecular pump.
Still yet another object of the invention is to provide a turbomolecular pump in which the exhaustion performance is exerted to the maximum extent for reducing losses when a temperature of a rotor blade is within an allowable value, a variation in an r.p.m. of a motor pump is lowered to maintain an exhaustion speed and an inlet port pressure at constant levels even though the gas load varies, and deterioration of the rotor blade caused by heat generation can be prevented when the temperature of the rotor blade exceeds the maximum allowable value.
Another object of the invention is to provide a turbomolecular pump which is forcibly cooled around rotor blade to thereby improve the exhaustion performance (allowable gas flow rate, allowable inlet port pressure).
In order to attain the above-noted objects, the invention according to one aspect thereof is characterized by comprising rotor blade temperature detecting means for measuring or estimating a temperature of the rotor blade (12). Provision of the rotor blade temperature detecting means to a turbomolecular pump P allows detection of the temperature of the rotor blade (12), thereby making it possible to use this temperature to increase the lifetime of the rotor blade (12) and to prevent deterioration caused by heat generation. In this case, the rotor blade temperature detecting means includes all means capable of measuring or estimating the temperature of the rotor blade (12).
Specifically, as an example of the rotor blade temperature detecting means, according to another aspect of the invention, it is characterized in that the rotor blade temperature detecting means is provided with a thermometer (1) facing the rotor blade (12), and being capable of detecting a temperature thereof in a non-contact manner therewith, the thermometer being embedded in a base portion (13) or disposed at a flange portion of an inlet port (40). The thermometer (1), is not brought into contact with the rotor blade (12) and is embedded in the base portion (13) or disposed at the flange portion of the inlet port (40). As a result, the temperature of the rotor blade (12) can be measured without affecting a flow of gas.
Further, as another example of the rotor blade temperature detecting means according to the invention, it is characterized in that the rotor blade temperature detecting means includes temperature detecting elements (84a, 84b, 84c) disposed at least one of a fixing blade (82) confronting the rotor blade (12) at a small interval, a fixing blade spacer (86) supporting one end of the fixing blade (82) and stacked step by step in a floating direction of the rotor blade (12), and a member (96) fixed to a stator (92) through at least one supporting portion (94) made of a thermally insulating material confronting a main shaft (104) of the rotor blade (12) and provided in a space formed at the rotor blade (12) side of the stator (92) one end of which is fixed to the base portion (13), and further comprises an arithmetic unit (98) for calculating and estimating a temperature of the rotor blade (12) based on the temperature detected by the temperature detecting elements (84a, 84b, 84c).
The rotor blade temperature detecting means includes temperature detecting elements (84a, 84b, 84c) disposed at at least one of a fixing blade (82), a fixing blade spacer (86), and a member (96) fixed to a stator (92) through a supporting portion (94), and arithmetically estimates a temperature of the rotor blade (12) based on the detected temperature. This arithmetic can be performed, in view of thermal conductivity, heat radiation and the like, to be rendered as a theoretical value, and, in addition, by being compared with experimental data calculated in advance, or the like. The provision at the fixing blade (82) or the like can measure the temperature of the rotor blade (12) without affecting a flow of gas in a similar manner as described above.
Further, as still another example of the rotor blade temperature detecting means according to the invention, it is characterized in that the rotor blade temperature detecting means comprises: first length measuring means for measuring lengths in a floating direction of the rotor blade (12) and calculating a variation in lengths before and after thermal expansion; second length measuring means for measuring lengths in a floating direction of a main shaft (104) of the rotor blade (12) and calculating a variation in lengths before and after the thermal expansion; and an arithmetic unit for calculating and estimating a temperature of the rotor blade (12) based on a difference between the variation in lengths by the second length measuring means and the variation in lengths by the first length measuring means.
The rotor blade (12) and the main shaft (104) of the rotor blade (12) are subjected to heat expansion according to a temperature change. Approximately, the variation in lengths can be considered substantially proportional to the temperature change. For this reason, a variation in lengths before and after thermal expansion for the rotor blade (12) is calculated, and then a variation in lengths before and after thermal expansion for the main shaft (104) of the rotor blade (12) is calculated. A difference between the both variations in lengths is calculated, and considering coefficients of the thermal expansion depending upon the materials making up of the respective parts, the temperature of the rotor blade (12) is estimated by computation. The temperature of the rotor blade (12) can therefore be measured without affecting a flow of gas described above a similar manner as in.
Further, as still another example of the rotor blade temperature detecting means according to the invention, it is characterized in that the rotor blade temperature detecting means arithmetically estimates a temperature of the rotor blade (12) based on a difference between a temperature of introduced gas at an inlet port (40) and an exhaust port (122) or based on a difference between a temperature at an entry (128) and a exit (130) of a water-cooled tube that is provided to water-cool the rotor blade (12).
The temperature of introduced gas is measured at an inlet port (40) and an exhaust port (122), to calculate a temperature difference therebetween. Or, a temperature is measured at an entry (128) and an exit (130) of a water-cooled tube that is placed close to the rotor blade (12) or around an outer casing (136) in order to water-cool the rotor blade (12), to thereby calculate a temperature difference therebetween. Based on the temperature difference, the temperature of the rotor blade (12) is then estimated by calorie computation, or by being compared with experimental data calculated in advance, or the like. A temperature of the rotor blade (12) can be therefore measured without affecting a flow of gas in a similar manner as described above.
The invention according to another aspect is characterized by comprising base temperature setting means for setting a target temperature of the base portion (13) based on the temperature of the rotor blade (12) calculated by the rotor blade temperature detecting means; temperature difference calculating means for calculating a difference between the target temperature of the base temperature setting means and the temperature measured in fact at the base portion (13); and temperature control means (27) for controlling to heat or cool the base portion (13) in response to an output signal of the temperature difference calculating means.
The base portion (13) is heated to prevent a deposition of generated products. For this purpose, a target temperature of the base portion (13) is set on the basis of the temperature of the rotor blade (12) calculated by the rotor blade temperature detecting means in order to prevent an abnormal increase of the temperature of the rotor blade (12). A difference between that target temperature and the temperature measured in fact at the base portion (13) is calculated, and whether the base portion (13) is heated or cooled is controlled based on this difference. This enables a deposition of generated products to be prevented while attaining a protection of the rotor blade (12).
Further, according to the invention as set forth in claim a turbomolecular pump, which comprises baking means for heating for a predetermined time period and then cooling at least one of the turbomolecular pump P, a pipe (42) one end of which is connected to an inlet port (40) of the turbomolecular pump P, and an external device (46) connected to the other end of the pipe (42) while the turbomolecular pump P is operated without introducing gas, is characterized by comprising: baking temperature setting means for setting a target temperature (54) of a rotor blade (12) for heating; temperature difference calculating means (52) for calculating a difference between the target temperature (54) of the rotor blade (12) in the baking temperature setting means and the temperature of the rotor blade (12) obtained by the rotor blade temperature detecting means (1); heating means (29, 50) for heating for a predetermined time period at least one of an outer casing (136) and a base portion (13) of the turbomolecular pump P, the pipe (42), and the external device (46) in response to an output signal of the temperature difference calculating means (52); and cooling means (51) for cooling at least one of the outer casing (136), the base portion (13), the pipe (42), and the external device (46) after a predetermined time elapses since heating performed by the heating means (29, 50).
The baking temperature setting means sets a target temperature (54) for heating when baking is performed. A difference between the target temperature (54) and the temperature of the rotor blade (12) obtained by the rotor blade temperature detecting means is calculated. At least one of an outer casing (136) and a base portion (13) of the turbomolecular pump P, a pipe (42), and an external device (46) is heated for a predetermined time period. The heated outer casing or the like is then inversely cooled after a predetermined time elapses since the heating. Therefore, an utmost pressure can be increased within a chamber while attaining a protection of the rotor blade (12).
Further, according to another aspect of the invention, the pump is characterized by comprising lifetime prediction means (63) for predicting a lifetime of the rotor blade (12) and/or a deposition volume of generated products by combining plural items among how the temperature of the rotor blade (12) obtained by the rotor blade temperature detecting means exceeds a predefined allowable value, how long it exceeds the allowable value, and the pressure within a pipe (42) one end of which is connected to the inlet port (40) or within an external device (46) connected to the other end of the pipe (42), to be output as a signal value; and discriminating means (65) for performing an alarm display (67) when the signal value of the lifetime prediction means (63) is compared with a predefined set value and then exceeds the set value, and/or at least one of a variable setting of the target temperature of the base temperature setting means and a variable setting of the target temperature of the rotor blade (12) in the baking temperature setting means, based on a difference between the signal value and the set value.
The degree is measured how the temperature of the rotor blade (12) obtained by the rotor blade temperature detecting means, exceeds a predefined allowable value. Methods of measuring the degree include evaluation methods such as ranking and weighting. Then, the period during which it exceeds the allowable value is measured. The pressure within the pipe (42) or the external device (46) is then measured. The lifetime prediction means (63) predicts a lifetime of the rotor blade (12) and/or a deposition volume of generated products by combining plural items among these.
The prediction of a lifetime of the rotor blade (12) and/or a deposition volume of generated products may be individually or concurrently implemented. Alternatively, the alarm display (67) may be performed by comparing the output of the lifetime prediction means (63) with the predefined set value, or, otherwise, the target temperature of the base temperature setting means may be set variable or the target temperature of the baking temperature setting means may be set variable, according to the difference in the comparison result. The variable setting of the target temperature of the base temperature setting means and the variable setting of the target temperature of the baking temperature setting means may be individually or concurrently implemented. With the foregoing arrangement, an alarm can be provided at the proper timing of an overhaul for the rotor blade (12) or to prevent deterioration of the rotor blade (12) caused by heat generation.
Further, according to another aspect of the invention, a turbomolecular pump in which a rotor blade driving motor M is driven by a motor driver (8), is characterized in that the temperature of the rotor blade (12) obtained by the rotor blade temperature detecting means is compared with a predefined set temperature, to make an output of the motor driver (8) variable and/or to make an r.p.m. of the rotor blade (12) variable, based on the difference therebetween.
The rotor blade temperature detecting means is provided for always detecting a temperature of the rotor blade (12). The detected temperature of the rotor blade (12) is compared with a predefined set temperature to calculate a difference therebetween. Based on the difference, the output of the motor driver (8) is then adjusted, or the r.p.m. of the rotor blade (12) is adjusted. This allows the output of the motor driver (8) or the r.p.m. of the rotor blade (12) to be adjusted while maintaining a temperature of the rotor blade (12) within a restricted range, and can improve the exhaustion performance.
Further, according to another aspect of the invention, a turbomolecular pump in which a rotor blade driving motor M is driven by a motor driver (8) is, characterized by comprising: motor driver output set r.p.m. determining means (5) for comparing a temperature of the rotor blade (12) obtained by the rotor blade temperature detecting means with a predefined set temperature and, based on the difference therebetween, determining a driver output and/or a set r.p.m. which may be exerted to the maximum to the rotor blade driving motor M; and at least one of driver output switching means (6) for adjusting a driving output of the motor driver (8) in a variable manner or stopping the motor M in response to the output signal of the motor driver output set r.p.m. determining means (5), and r.p.m. compensating means (11) for comparing the set r.p.m. calculated by the motor driver output set r.p.m. determining means (5) with an output signal of an r.p.m. sensor (2) for detecting an r.p.m. of the rotor blade driving motor M, to drive the motor driver (8) based on the difference therebetween.
With such an arrangement, when a temperature of the rotor blade (12) is within an allowable value, the driving output of the motor driver (8) can be made variable by changing over the driver output switching means (6) in response to the signal of the motor driver output set r.p.m. determining means (5). The set r.p.m. of the rotor blade driving motor M can also be made variable. This allows the driving output and/or the set r.p.m. to be improved and the exhaustion performance (vacuum performance) of the turbomolecular pump P to be exerted to the maximum, thereby reducing losses.
If it is so modified in this way that the driving output of the motor driver (8) is increased and the set r.p.m. of the motor driver (8) is improved, the increased driving output or set r.p.m. (improved gas exhaustion performance) allows a variation in the r.p.m. of the rotor blade driving motor M pump to be lowered, and the exhaustion performance to be maintained even though the gas load is changed.
However, when a temperature of the rotor blade (12) exceeds an allowable value, the driver output switching means (6) permits the driving output of the motor driver (8) to be lowered or the brake, etc. to be applied in a worst case (although a variety of stopping techniques including shifting phases in current may be contemplated, any technique may be available). As an alternative, the r.p.m. compensating means (11) reduces the set r.p.m., thereby lowering a frequency of impinging the gas molecules on the rotor blade (12). The foregoing arrangement enables the temperature of the rotor blade to be reduced and deterioration of the rotor blade (12) caused by heat generation to be prevented. While either the driver output switching means (6) or the r.p.m. compensating means (11) may be employed, both of these means may be used in combination. The combined use of both means makes it possible to further improve precision of the exhaustion performance.
Further, another aspect of the invention is characterized in that a determination of the driver output and/or the set r.p.m. by the motor driver output set r.p.m. determining means (5) is adjusted by feeding back a detection signal detected by at least one sensor of an r.p.m. sensor (2) for detecting an r.p.m. of the rotor blade driving motor M, a motor current sensor (3) for detecting motor current of the rotor blade driving motor M, and an axial electromagnet current sensor (4) for detecting a current running toward an axial electromagnet that causes the rotor blade (12) to magnetically float.
Output signals of the r.p.m. sensor (2), the motor current sensor (3), and the axial electromagnet current sensor (4) vary correspondingly to a change in the gas load. It is therefore appropriate that an output signal of at least one of these sensors is fed back to adjust the driver and/or to adjust the set r.p.m. This enables a prompt adjustment of the driver output and/or adjustment of the set r.p.m., while keeping the temperature of the rotor blade (12) within the allowable value.
Further, another aspect of the invention is characterized in that a determination of the driver output and/or the set r.p.m. by the motor driver output set r.p.m. determining means (5) is carried out based on an external signal (15) predicting a change in a load flow rate from the external device (46) connected to the inlet port (40) of the turbomolecular pump P.
The arrangement in which the external signal is input makes it possible to set the driver output or the set r.p.m. of the motor driver (8) higher in advance, in response to the external signal from, from example, semiconductor manufacturing equipment, etc., before the gas load is increased. This allows the exhaustion performance to be maintained even with an abrupt increase of the gas load caused by releasing a gate valve (44) or the like.
Further, another aspect of invention is characterized by comprising rotor blade temperature discriminating means (73) for discriminating whether or not the temperature of the rotor blade (12) obtained by the rotor blade temperature detecting means exceeds a predefined allowable value; and cooling means (51) for cooling a surrounding area close to the rotor blade (12) or a surrounding area of the outer casing based on an output of the rotor blade temperature discriminating means (73).
A difference between the temperature of the rotor blade (12) obtained by the rotor blade temperature detecting means and a predefined allowable value is found, and then, based on the difference, a water-cooled tube or the like is used to cool around adjacent to the rotor blade (12) or around the outer casing. It can be therefore realized to further increase a gas flow rate and to improve a TMS temperature.